The present invention relates to a motor control device for controlling an AC motor.
A high-output motor used for powering an electric vehicle, hybrid vehicle, or the like is driven at a high voltage. Since a DC battery is mounted as a power source mounted in such a vehicle, the current is converted into a three-phase AC current by an inverter circuit that uses a switching element such as an insulated gate bipolar transistor (IGBT). A signal for driving the inverter circuit, e.g. a drive signal for driving a gate of the IGBT, is generated in a control circuit of a low-voltage circuit that is insulated from a high-voltage circuit driving the motor, and operates at a much lower voltage than that of the high-voltage circuit.
Accordingly, a motor control device driving the motor is provided with an IGBT drive circuit for driving the IGBT of the inverter circuit based on the drive signal. In other words, as illustrated in FIG. 6, the motor control device is structured having a motor control circuit 300 that operates within the low-voltage circuit; an IGBT drive circuit 200 that operates within the high-voltage circuit and drives the IGBT based on a drive signal generated by the motor control circuit 300; and an inverter circuit 100 that is structured from a plurality of IGBTs.
The inverter circuit 100 generating a three-phase AC current is structured from six IGBTs. The respective IGBTs operate independently, and gate drive circuits for driving the gates of the IGBTs are thus provided mutually independent in the IGBT drive circuit 200. Since the IGBTs handle a high voltage, the gate drive circuits driving the IGBTs must be arranged having a suitable insulation distance.
Japanese Patent Application Publication No. JP-A-2006-280148 (paragraphs 13 and 15, FIG. 1, etc.) discloses a voltage control device that is provided with a plurality of gate drive circuits for driving a plurality of IGBTs. According to JP-A-2006-280148 a control circuit and the gate drive circuit are disposed at least separated by an insulation distance that corresponds to a distance between an input pin and an output pin of a transformer. The gate drive circuits are also disposed separated by a predetermined insulation distance.